         [dead-w, alive-w] (rsplit-by n-young-women mortality-women)
         [grown-m, _]      (rsplit-by alive-m 0.25)
         [grown-w, _]      (rsplit-by alive-w 0.25)]
-    (fact :young-men-dead {:tribe (.id tribe) :n dead-m})
-    (fact :young-women-dead {:tribe (.id tribe) :n dead-w})
-    (fact :young-men-grew-old {:tribe (.id tribe) :n grown-m})
-    (fact :young-women-grew-old {:tribe (.id tribe) :n grown-w})
+    (when (> dead-m 0)
+      (fact :young-men-dead {:tribe (.id tribe) :n dead-m}))
+    (when (> dead-w 0)
+      (fact :young-women-dead {:tribe (.id tribe) :n dead-w}))
+    (when (> grown-m 0)
+      (fact :young-men-grew-old {:tribe (.id tribe) :n grown-m}))
+    (when (> grown-w 0)
+      (fact :young-women-grew-old {:tribe (.id tribe) :n grown-w}))
     (Population. 0 (* -1 (+ dead-m grown-m)) (* -1 (+ dead-w grown-w)) grown-m grown-w)))
 
 (defn update-old-population

        men-availability-factor (men-availability-factor young-men young-women)
        women-fertility         (* young-women 1.1 (perturbate-high prosperity))
        births                  (round (* women-fertility men-availability-factor))]
    (fact :births {:tribe (.id tribe) :n births})
    (Population. births 0 0 0 0)))

(defn update-children

        n-old-women (-> tribe :population :old-women)
        [dead-m, alive-m] (rsplit-by n-old-men mortality-men)
        [dead-w, alive-w] (rsplit-by n-old-women mortality-women)]
    (when (> dead-m 0)
      (fact :old-men-dead {:tribe (.id tribe) :n dead-m}))
     (when (> dead-w 0)
      (fact :old-women-dead {:tribe (.id tribe) :n dead-w}))
    (Population. 0 0 0 (* -1 dead-m) (* -1 dead-w))))


